Transmission of wireless neural signals through a 0.18µm CMOS low-power amplifier

Abstract

Abstract-In the field of Brain Machine Interfaces (BMI) researchers still are not able to produce clinically viable solutions that meet the requirements of long-term operation without the use of wires or batteries. Another problem is neural compatibility with the electrode probes. One of the possible ways of approaching these problems is the use of semiconductor biocompatible materials (silicon carbide) combined with an integrated circuit designed to operate with low power consumption. This paper describes a low-power neural signal amplifier chip, named Cortex, fabricated using 0.18µm CMOS process technology with all electronics integrated in an area of 0.40mm 2 . The chip has 4 channels, total power consumption of only 144µW, and is impedance matched to silicon carbide biocompatible electrodes. I. INTRODUCTIONAlthough research with Brain Machine Interfaces (BMI) has evolved with great speed in recent years, researchers still do not have reliable BMI systems, which has prevented widespread clinical testing and, ultimately, assisting individuals with neurological and physical disabilities.In order for BMI to effectively make use of the advances in robotic and computer technology, it is vital to find a biological interface that meets the requirements of long-term electrical reliability, low-power operation, and biocompatibility. These requirements are of special importance. First, commonplace systems are based on batteries that eventually discharge and must be replaced after short periods of time, resulting in additional maintenance requirements; Second, many systems rely on materials that may not have reliable biocompatibility, and can possibly erode with time, demanding costly and high-risk replacement procedures [1][2]. In this paper, our contribution focuses on addressing these two issues.This project describes the development of a wireless BMI system -see Figure 1, with constraints of very low-power consumption and biocompatibility. Our solution relies on two features: (1) we use a chip designed to operate with a power consumption that is small enough for it to be powered by radio frequency antennas, dispensing with the need for batteries; (2) we use a probe manufactured from silicon carbide (SiC), a material that demonstrated excellent neural compatibility with murine mouse brain tissue in vivo [13]. This paper presents the first version of the Cortex chip, which is a 4-channel amplifier that magnifies neural signals to levels high enough for them to be processed by a computer. Fig. 1. Conceptual diagram of the proposed BMI system, which integrates the Cortex chip, described in detail in this paper, with cubic silicon carbide electrodes (3C-SiC) and an RFID wireless interface. II. CONCEPTS AND RELATED WORKS A. Gliosis and Neural ImplantsThe introduction of neural interfaces inside the central nervous system (CNS) inevitably damages the delicate tissue which leads to the neural inflammitory response, gliosis [1][2][3][4][5]. Gliosis is a reactive cellular process concerning physiological changes in glial cell...

SiC for Biomedical Applications

“…The 4 channel speed is up to 800 kbps, using a 10-bit, 20kHz analog to digital conversion, in accordance to the max specific absorption rate (1.6W/kg) defined by the Federal Communications Commission. Summary of the results for the Cortex chip in comparison with published results for similar circuits may be found in [11], where it is shown that our chip has the following advantages: better PSRR and power consumption performance; smaller area per channel; AC instead of DC coupling compared with off-the-shelf chips.…”

“…Fig. 4 shows one such low-power neural signal amplifier chip, named Cortex, fabricated using 0.18µm CMOS process technology integrated in an area of 0.40 mm 2 [11]. The chip has 4 channels, total power consumption of only 144µW, and is impedance matched to our SiC implantable neural interface electrodes.…”